Computerized sewing devices are known in the art. Two pieces to be sewn together are placed on a work holder and moved by an X-Y table in the necessary directions for the desired sewing path.
Since the sewing path is pre-programmed and carried out by machine, it is possible that the sewn pieces will move from the ideal position for sewing. This can be caused by improper placement on the work holder, by deformation due to environmental conditions or by deformation due to the sewing process itself. To solve this problem, edge detecting means have been added to the sewing apparatus. These include devices according to U.S. Pat. Nos. 4,834,008 and 4,784,071 to the same applicants, which include cameras and illumination means for scanning the instantaneous location of the sewn edge by utilizing its shadow, comparing it with the expected location, and adjusting the sewing path in real time in accordance with the scanning determination.
These methods serve very well to identify the edge of the sewn piece and to provide instantaneous correction of the sewing path when necessary, thereby compensating, accurately for all the causes of edge variation.
However, this ideal solution requires overall precision in the x-y table and other components for exact correction in real time, resulting in relatively costly components being required.
This method of edge detection is sufficient, in most cases. However, certain combinations of materials and textures pose problems in applying this method, requiring, in order to identify the edge in the field of view, that the algorithm be changed to one which is very complicated and slow.